This invention relates to transformers and more particularly to transformers with a disc wound coil.
As is well known, a transformer converts electricity at one voltage to electricity as another voltage, either of higher or lower value. A transformer achieves this voltage conversion using a primary coil and a secondary coil, each of which is wound on a ferromagnetic core and comprise a number of turns of an electrical conductor. The primary coil is connected to a source of voltage and the secondary coil is connected to a load. The ratio of turns in the primary coil to the turns in the secondary coil (“turns ratio”) is the same as the ratio of the voltage of the source to the voltage of the load. Two main winding techniques are used to form coils, namely layer winding and disc winding. The type of winding technique that is utilized to form a coil is primarily determined by the number of turns in the coil and the current in the coil. For high voltage windings with a large number of required turns, the disc winding technique is typically used, whereas for low voltage windings with a smaller number of required turns, the layer winding technique is typically used.
In the disc winding technique, the conductor turns required for a coil are wound in a plurality of discs serially disposed along the axial length of the coil. In each disc, the turns are wound in a radial direction, one on top of the other, i.e., one turn per layer. The discs are connected in a series circuit relation and are typically wound alternately from inside to outside and from outside to inside so that the discs can be formed from the same conductor. An example of such alternate winding is shown in U.S. Pat. No. 5,167,063.
A transformer with disc windings may be dry, i.e., cooled by air as opposed to a liquid dielectric. In such a dry transformer, the disc windings may be coated with, or cast in, a dielectric resin using vacuum chambers, gelling ovens etc. If the disc windings are cast in a solid dielectric resin, cooling issues are raised. In order to address these issues, U.S. patent application Ser. No. 11/494,087 to Pauley et al. (which is assigned to the assignee of this application and is hereby incorporated by reference) discloses using pre-formed cooling ducts to provide cooling. The present invention is directed toward improvements in the construction, installation and use of such pre-formed cooling ducts in a cast resin transformer having disc windings.